On Mon, Nov 23, 2020 at 10:49:38PM -0800, Chris Goldsworthy wrote:
> +static void __evict_bh_lru(void *arg)
> +{
> + struct bh_lru *b = &get_cpu_var(bh_lrus);
> + struct buffer_head *bh = arg;
> + int i;
> +
> + for (i = 0; i < BH_LRU_SIZE; i++) {
> + if (b->bhs[i] == bh) {
> + brelse(b->bhs[i]);
> + b->bhs[i] = NULL;
> + goto out;
That's an odd way to spell 'break' ...
> + }
> + }
> +out:
> + put_cpu_var(bh_lrus);
> +}
...
> @@ -3245,8 +3281,15 @@ drop_buffers(struct page *page, struct buffer_head
> **buffers_to_free)
>
> bh = head;
> do {
> - if (buffer_busy(bh))
> - goto failed;
> + if (buffer_busy(bh)) {
> + /*
> + * Check if the busy failure was due to an
> + * outstanding LRU reference
> + */
> + evict_bh_lrus(bh);
> + if (buffer_busy(bh))
> + goto failed;
Do you see any performance problems with this? I'm concerned that we
need to call all CPUs for each buffer on a page, so with a 4kB page
and 512-byte block, we'd call each CPU eight times (with a 64kB page
size and 4kB page, we'd call each CPU 16 times!). We might be better
off just calling invalidate_bh_lrus() -- we'd flush the entire LRU,
but we'd only need to do it once, not once per buffer head.
We could have a more complex 'evict' that iterates each busy buffer on a
page so transforming:
for_each_buffer
for_each_cpu
for_each_lru_entry
to:
for_each_cpu
for_each_buffer
for_each_lru_entry
(and i suggest that way because it's more expensive to iterate the buffers
than it is to iterate the lru entries)
